Adsorption of Nitrilotriacetate (NTA), Co and CoNTA By Gibbsite

Abstract

Abstract--Adsorption of Co 2 § nitrilotriacetic acid (NTA) and equal-molar Co 2 § and NTA by a low surface area (LSA) commercial gibbsite (3.5 m 2 g-~) was investigated in batch as a function of pH (4.5 to 10.5), adsorbate (0.5 to 10 txM) and adsorbent (0.5 to 75 g L ~) concentrations and ionic strength (0.01 to 1 M NaC104). The adsorption of Co 2 § (Co-only) and the acid form of NTA (NTA-only) by gibbsite in 0.01 M NaC104 exhibit cation-like and anion-like adsorption edges, respectively. For the equal-molar CoNTA chelate, Co and NTA adsorption edges were similar but not identical to the Co-only and NTAonly edges. Differences suggest the existence of a ternary CoNTA surface complex with the Co in the intact chelate coordinated to surface hydroxyls. NTA-only adsorption was insensitive to ionic strength variation, indicating weak electrostatic contributions to surface coordination reactions. This is consistent with the formation of inner-sphere surface NTA complexes and ligand exchange reactions in which monodentate, bidentate and binuclear NTA surface complexes form. Cobalt adsorption increases (edge shifts to lower pH by 1 pH unit) on LSA gibbsite as ionic strength increases from 0.01 to 1 M NaC104. For the same ionic strength change, a similar shift in the Co-only edge was observed for another commercial gibbsite (16.8 m 2 g 1); however, no change was observed for ~-A1203. Ionic strength shifts in Co 2+ adsorption by gibbsite were described as an outer-sphere CoOH § surface complex using the triplelayer model. Results suggest that, at waste disposal sites where 6~ and NTA have been co-disposed, NTA will not promote ligand-like adsorption of Co for acid conditions, but will reduce cation-like adsorption for basic conditions. Thus, where gibbsite is the dominant mineral sorbent, NTA will not alter 6~ mobility in acidic pore waters and groundwaters; however, NTA could enhance 6~ mobility where alkaline conditions prevail, unless microbial degradation of the NTA occurs.

Adsorption of Phosphonates onto the Goethite–Water Interface

“…NTMP adsorption increases with decreasing pH. There is no influence of the background NaNO 3 concentration on the adsorption in the range from 1 mM to 1 M NaNO 3 . Whereas the presence of an ionic strength effect does not necessarily mean that outer-sphere complexes are formed, the absence of an effect points clearly toward an inner-sphere complex (33).…”

“…Lövgren et al (27) reported surface site density, first and second protonation constants, and total specific capacitance values for their goethite preparation in 0.10 M NaNO 3 . It is assumed that these same values (shown in Table 2) also apply to our goethite preparation in 0.010 M NaNO 3 .…”

“…While monocarboxylic acids exhibit only weak adsorption, increasing the number of carboxylic acid groups leads to increased adsorption (1). Aminocarboxylate compounds which are able to effectively complex Fe(III) or Al(III) in solution such as NTA or EDTA display a strong adsorption onto the respective (hydr)oxide surfaces (2)(3)(4).…”

Adsorption of heavy metal ions on soils and soils constituents

“…For trivalent metals such as Co(III) and Cr(III), hexadentate complexes are formed [105]. Although the modelling studies assume a direct, inner-sphere bonding where the interactions with the surface are dominated by the chelating abilities of EDTA, FTIR spectroscopy and EXAFS showed no indications of inner-sphere complexation between Pb-EDTA and goethite [111]. Spectra confirmed hexadentate coordination between the EDTA and Pb but exhibited no evidence of EDTA-Fe-specific interactions.…”

Dissimilatory bacterial reduction of Al-substituted goethite in subsurface sediments

“…The 0.5 N HCl extraction displaces weakly and strongly adsorbed inorganic cations on oxides and clays; and dissolves acid-soluble ferrous iron phases such as siderite, fine-grained magnetite, and green rust , and fine-grained Al(III) oxides (Girvin et al, 1996). It will also dissolve some Al(III) from fine-grained kaolinite, which is a component of the Eatontown sediment.…”